[Patent reference 1] JP, 4-15735, B
[Patent reference 2] JP, 10-81012, A
An ink jet head for discharging an ink drop is used by an ink jet recording device serving image formation apparatuses, such as printers, facsimile apparatuses, copiers, and plotters. As the ink jet head, products based on various technologies have been available, such as a piezo type product wherein an ink drop is discharged by deforming a diaphragm that constitutes a partition of an ink passage (pressurized ink chamber) by a piezoelectric device serving as pressure generating means for generating pressure for pressurizing ink in the ink passage such that the volume of the ink chamber is changed, a thermal type product wherein an ink drop is discharged by generating air bubbles by heating the ink in the pressurized ink chamber using an exothermic resistor, and an electrostatic product wherein an ink drop is discharged by changing the volume of the pressurized ink chamber by deforming a diaphragm by an electrostatic force applied between the diaphragm and an electrode that opposes the diaphragm.
For driving the ink jet head, there are two methods. Namely, one is called a “push and strike” method whereby an ink drop is discharged by reducing the volume of the pressurized ink chamber by pushing the diaphragm toward the pressurized ink chamber, and a “pull and strike” method whereby an ink drop is discharged when the diaphragm that is first pulled out is made to return to its original position.
Further, a method of forming a large ink drop is disclosed by Patent reference 1 wherein two or more minute ink drops, i.e., ink droplets, are sequentially discharged, and the ink droplets merge before reaching a recording medium (paper form) to form a large ink drop.
In addition, an apparatus that is capable of gradation printing is disclosed by Patent reference 2 wherein a first drive pulse discharges a first ink drop, and a second drive pulse discharges a second ink drop, dimensions of which are different from the first ink drop; and more than four gradation steps are made available by combining the first and the second drive pulses.